feat(client): pay v2 支付渠道 switch + 订单列表/详情端到端

购买/支付(Phase B):
- 新 SegSwitch 段控 widget(镜像 .segswitch 原子)
- 购买页重构:顶部支付渠道 switch(默认 USDT→加密货币 / 人民币→支付宝),套餐价随渠道分币种显示,删底部弹窗选方式;点购买直达支付页
- 支付页加订单信息卡(套餐/渠道/金额按币种)
- models:PayChannel + PayCatalogItem.priceUsdtMicro/priceLabel(ch)/perMonthLabel(ch)

订单(P0,全新):
- payment_api.listOrders() + orders_provider(列表 + 详情 family)
- OrdersScreen 列表→详情(状态 pill / 可复制订单号 / 继续支付·重新购买)
- 导航:NavView.orders + desktop_shell 分支 + account 入口

配套:
- l10n +19 getter(支付渠道 4 + 订单 15)×6 语言,l10n 闸绿
- 图标单源迁移 lucide_icons_flutter + pangolin_icons.dart(codegen)
- 联系渠道订正(Telegram/邮件 support@yanmeiai.com/官网) + 前端去广告&时长
- 测试:购买 switch 分币种 + 订单列表/空态/详情 + 假 API listOrders;golden 重录
- flutter analyze 0 error,flutter test 226 全绿

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013nMthbVEmQquxBRKb9Fj8u

client/lib/models/payment.dart

@@ -1,6 +1,15 @@
 // payment.dart — pay v2 支付领域模型(server 代理端点的响应形状)。
 // 金额只读展示:price_minor 为 CNY 分;crypto 精确金额在 session.payload 里。
 
+/// 支付渠道:结算币种即支付方式(一步定)。usdt→加密货币 / cny→支付宝。
+/// 各币种一口价(不做实时汇率换算);实际扣款以 pay 侧为准。
+enum PayChannel { usdt, cny }
+
+extension PayChannelX on PayChannel {
+  String get currency => this == PayChannel.usdt ? 'USDT' : 'CNY';
+  String get method => this == PayChannel.usdt ? 'crypto' : 'alipay';
+}
+
 class PayCatalogItem {
   const PayCatalogItem({
     required this.sku,
@@ -8,13 +17,15 @@ class PayCatalogItem {
     required this.days,
     required this.priceMinor,
     required this.currency,
+    this.priceUsdtMicro = 0,
   });
 
   final String sku;
   final String plan;
   final int days;
-  final int priceMinor;
-  final String currency;
+  final int priceMinor;      // CNY 分(展示)
+  final String currency;     // CNY
+  final int priceUsdtMicro;  // USDT 微元(展示;各币种一口价)
 
   factory PayCatalogItem.fromJson(Map<String, dynamic> j) => PayCatalogItem(
         sku: j['sku'] as String,
@@ -22,9 +33,70 @@ class PayCatalogItem {
         days: (j['days'] as num?)?.toInt() ?? 0,
         priceMinor: (j['price_minor'] as num?)?.toInt() ?? 0,
         currency: j['currency'] as String? ?? 'CNY',
+        priceUsdtMicro: (j['price_usdt_micro'] as num?)?.toInt() ?? 0,
       );
 
-  String priceLabel() => '¥${(priceMinor / 100).toStringAsFixed(2)}';
+  /// 约当月数(31→1 / 92→3 / 366→12),用于每月折算展示。
+  int get months {
+    final m = (days / 30.4).round();
+    return m < 1 ? 1 : m;
+  }
+
+  /// 按渠道币种给总价文案(USDT $ / CNY ¥)。
+  String priceLabel(PayChannel ch) => ch == PayChannel.usdt
+      ? '\$${(priceUsdtMicro / 1000000).toStringAsFixed(2)}'
+      : '¥${(priceMinor / 100).toStringAsFixed(2)}';
+
+  /// 按渠道币种给每月折算文案(不含 /月 后缀,后缀由 l10n 提供)。
+  String perMonthLabel(PayChannel ch) => ch == PayChannel.usdt
+      ? '\$${(priceUsdtMicro / 1000000 / months).toStringAsFixed(2)}'
+      : '¥${(priceMinor / 100 / months).toStringAsFixed(2)}';
+}
+
+/// PayOrderSummary — 订单列表项(server orderView 台账视图)。
+/// 金额为结算币种 minor:CNY 分 / USDT 微元。
+class PayOrderSummary {
+  const PayOrderSummary({
+    required this.orderNo,
+    required this.sku,
+    required this.plan,
+    required this.days,
+    required this.method,
+    required this.status,
+    required this.amountMinor,
+    required this.currency,
+    required this.createdAt,
+    this.paidAt,
+  });
+
+  final String orderNo;
+  final String sku;
+  final String plan;
+  final int days;
+  final String method;      // crypto | alipay | nezha …
+  final String status;      // created | paid | canceled(本地台账)
+  final int amountMinor;
+  final String currency;    // CNY | USDT
+  final DateTime? createdAt;
+  final DateTime? paidAt;
+
+  factory PayOrderSummary.fromJson(Map<String, dynamic> j) => PayOrderSummary(
+        orderNo: j['order_no'] as String? ?? '',
+        sku: j['sku'] as String? ?? '',
+        plan: j['plan'] as String? ?? 'pro',
+        days: (j['days'] as num?)?.toInt() ?? 0,
+        method: j['method'] as String? ?? '',
+        status: j['status'] as String? ?? '',
+        amountMinor: (j['amount_minor'] as num?)?.toInt() ?? 0,
+        currency: j['currency'] as String? ?? 'CNY',
+        createdAt: j['created_at'] == null ? null : DateTime.tryParse(j['created_at'] as String),
+        paidAt: j['paid_at'] == null ? null : DateTime.tryParse(j['paid_at'] as String),
+      );
+
+  /// 结算币种金额文案(USDT 6 位、CNY 2 位)。
+  String amountLabel() => currency == 'USDT'
+      ? '\$${(amountMinor / 1000000).toStringAsFixed(2)}'
+      : '¥${(amountMinor / 100).toStringAsFixed(2)}';
 }
 
 class PaySession {
@@ -53,23 +125,29 @@ class PayOrder {
       );
 }
 
+/// PayOrderStatus — 查单/详情响应。轮询只用 activated;订单详情页额外用
+/// 台账富字段(server GetOrder 现回带 orderView 全字段)。
 class PayOrderStatus {
   const PayOrderStatus({
     required this.orderNo,
     required this.payStatus,
     required this.activated,
     this.expiresAt,
+    this.summary,
   });
 
   final String orderNo;
   final String payStatus;
   final bool activated; // server 台账已消费 = 权益已开通(轮询成功判据)
   final DateTime? expiresAt;
+  final PayOrderSummary? summary; // 台账富字段(sku/plan/method/金额/时间…);详情页用
 
   factory PayOrderStatus.fromJson(Map<String, dynamic> j) => PayOrderStatus(
         orderNo: j['order_no'] as String? ?? '',
         payStatus: j['pay_status'] as String? ?? '',
         activated: j['activated'] as bool? ?? false,
         expiresAt: j['expires_at'] == null ? null : DateTime.tryParse(j['expires_at'] as String),
+        // 详情端点回带台账字段(列表端点同形);sku 存在才解析。
+        summary: j['sku'] == null ? null : PayOrderSummary.fromJson(j),
       );
 }